1. Field of the Invention
The present invention relates to a polysulfone, an electrolyte membrane using the same, and a fuel cell using the electrolyte membrane.
2. Description of the Related Art
Perfluorinated polymers are typically used as membranes in fuel cells, have a high thermochemical stability, and a high ionic conductivity. However, at an operating temperature of 100° C. or more, the ionic conductivity of perfluorinated polymers is substantially decreased because water in the membranes evaporates. In general, fuel cells operating at high temperatures of 100° C. or more, are subjected to less CO catalyst poisoning than fuel cells operating at lower temperatures, and have high catalyst activity, and therefore, a high output. In addition, the water used in fuel cells operating at high temperatures can be easily handled, and the miniaturization of fuel cells can be easily achieved. Perfluorinated polymer membranes are widely used in the field due to their high thermochemical stability and excellent mechanical properties. However, perfluorinated polymer membranes are limited to use at 100° C. or less, because the water, used in the perfluorinated polymer membranes to convey hydrogen ions, evaporates at high temperatures, and thus the ionic conductivity of the perfluorinated polymer membranes is substantially decreased. This problem can be overcome by the addition of heteropolyacid or by the formation of a composite membrane by using an inorganic material, such as SiO2.
When a composite membrane formed with heteropolyacid is used in a fuel cell, the fuel cell has an increased operating temperature. However, the heteropolyacid dissolves in water. In addition, the composite membrane has a low water retaining ability at 130° C., or more, thus decreasing the ionic conductivity of the membrane at such temperatures.
U.S. Pat. No. 5,525,436 discloses a gel-type membrane that operates at high temperatures and has polybenzimidazole complexed with a strong acid, such as a phosphoric acid or sulfuric acid. Such an acid conducts hydrogen instead of water. Although such gel-type electrolyte membranes show higher hydrogen ion conductivity, as the amount of the strong acid increases, improvements in the hydrogen ion conductivity of the gel-type electrolyte membrane are still needed.